1. Field of the Invention
The present invention relates to a method for transmitting control frames and user data frames in a mobile radio communication system.
2. Discussion of Related Art
In a CDMA (Code Division Multiple Access) mobile radio communication system, it is prescribed in a Radio Link Protocol (RLP) of IS-707.2 of February 1998 a relay layer corresponding to a radio section between a terminal device and a base station, for the sake of a circuit data service or a packet data service.
RLP frames can be classified into two types, control frames and user data frames. The user data frames transport user traffic data while the control frames are used to send control information required for RLP initialization and error recovering. The control frames contain important information in RLP operation. As a result, if reliability were not ensured for these control frames, it would negatively impact the performance of an overall system. According to the RLP retransmission procedure, the NAK (Negative Acknowledgement) RLP control frame for a particular user data frame can be transmitted more than once at the same time to ensure the reliability and the missing user data frame will be retransmitted whenever it receives the NAK frame.
Currently, the transmission methods of the NAK control frames in RLP type 1 and RLP type 2 will be described hereinafter.
When an entity receiving RLP frames or an RLP destination transmits NAK control frames for incorrect or lost user data frames, an entity sending RLP or an RLP source retransmits RLP user data frames whenever it receives the NAK control frames. For example, if the RLP source receives two NAK control frames containing the same missing sequence number, it retransmits the missing user data frames twice. In other words, the total number of the retransmission of RLP user data frames matches exactly the total number of NAK frames transmitted containing the sequence number of that user frame.
The above method has a drawback in terms of flexibility. For example, in case of simultaneous voice and packet data service such as the service option VPI, it may occur that the NAK control frames can not be transmitted over a forward channel (FCH) due to a voice packet transmission. In this case, the NAK control frames could be transmitted over a supplemental channel (SCH) with a low frame error rate (FER).
Referring to FIG. 2 showing a structure of the conventional RLP NAK control frame, it is constructed in the RLP NAK control frame by a data frame sequence number field SEQ with a length of 8 bits, a control field CTL with a length of 8 bits, a field FIRST with a length of 8 bits, a field LAST of a length of 8 bits, a frame check sequence field FCS with a length of 16 bits and a field, padding, with a variable length. The control field CTL is made up of a higher rank 4 bits and a lower rank 4 bits. If a value of the higher rank 4 bits is xe2x80x9c1100xe2x80x9d, it represents that the RLP control frame is the NAK frame and it requests to retransmit data frames. At this time, the lower rank 4 bits of the control field CTL is xe2x80x9c0000xe2x80x9d. A value xe2x80x9c11010000xe2x80x9d of the field CTL indicates a non-encrypted mode synchronization, a value xe2x80x9c11010011xe2x80x9d represents an encrypted mode synchronization, a value xe2x80x9c11100000xe2x80x9d provides a non-encrypted mode acknowledgement, a value xe2x80x9c11100011xe2x80x9d means an encrypted mode acknowledgement, a value xe2x80x9c11110000xe2x80x9d indicates a non-encrypted mode synchronization/acknowledgement, and a value xe2x80x9c11110011xe2x80x9d represents an encrypted mode synchronization/acknowledgement.
The field FIRST represents the 8 bit sequence number of a first data frame for which a retransmission is required. The field FIRST is used only in case of an NAK and its value is xe2x80x9c00xe2x80x9d except such case. The field LAST indicates the 8 bit sequence number of a last data frame for which the retransmission is required. The field LAST is also used only in case of the NAK and its value becomes xe2x80x9c00xe2x80x9d except such case.
The field FCS is a frame check sequence, the contents will be generated by 16 bits FCS polynomial specified in 3.1 of RFC 1662. The field FCS shall cover the fields SEQ, CTL, FIRST and LAST. The field, padding, is padding bits and it is required to fill the remainder of the frame. These bits shall be set to xe2x80x9c0xe2x80x9d.
In the conventional method for transmitting the RLP NAK control frames, in case that the number of sequence numbers of basically valid frames are more than the number of sequence numbers anticipated in the receiving station, NAK control frames for user data frames not received to the receiving station are required.
Referring to FIG. 3, when the receiving station receives user data frames with sequence numbers 1,2,3, a sequence number V(N) necessary by the receiving station and a sequence number V(E) estimated by the receiving station become xe2x80x9c4xe2x80x9d. V(R) shown in FIG. 3 indicates received sequence numbers. If a frame error rate (FER) becomes high owing to various causes of a radio section, the receiving station may receive a user data frame of a sequence number 14 instead of the user data frame of the sequence number 4. The receiving station may actually receive user data frames having more sequence numbers than the sequence number 14 since there is much possibility for a burst occurrence of the FER on the radio section. Like this, in case the receiving station receives the user data frame having the sequence number 14, the receiving station sends NAK control frames requiring for user data frames of missed sequence numbers 4 to 13 to the transmitting station. That is, the receiving station requests the transmitting station to retransmit the missed user data frames thereto. At this time, the receiving station operates of each retransmission counter for an NAK about the user data frames having the sequence number 4 to 14. After that, the number of the retransmission counter increases whenever an effective idle frame or a new effective data frame is received.
In case the receiving station does not receive the missed user data frames even till the retransmission counter for the NAK reaches a given threshold, the receiving station requires the retransmission of the missed user data frames from the transmitting station. In other words, the receiving station transfers NAK control frames to the transmitting station A. If user data frames of sequences numbers 5,8,9,11,13 are received before the timer of the NAK retransmission counter is expired, the NAK timer does not operate for the frames of the sequence numbers 5,8,9,11,13 any more. Then, the receiving station B retransmits NAK control frames only for user data frames not received even by the retransmission of the transmitting station A, to the transmitting station A.
That is to say, an NAK control frame is sent for the user data frame of the sequence number 4 shown in FIG. 3, and after 20 ms, the NAK control frame is resent for the user data frame of the sequence number 4. Also, NAK control frames are sent for the user data frames of sequence numbers 6, 7, and after 20 ms, the NAK control frames are resent for the user data frames of the sequence numbers 6, 7. And then, after 20 ms, an NAK control frame is transmitted for a user data frame of a sequence number 10, and after 20 ms, the NAK control frame is retransmitted for the user data frame of the sequence number 10. Also after 20 ms, an NAK control frame is transferred for a user data frame of a sequence number 12, and after 20 ms, the NAK control frame is retransferred for the user data frame of the sequence number 12 to the transmitting station A.
Supposing that, after the transmission of all the NAK control frames, the receiving station B receives only the user data frame of the sequence number 7 till the NAK timer is expired, the receiving station B again sends the NAK control frames for the respective user data frames having the missed sequence numbers 4,6,10,12 each three times to the transmitting station A. In response to such operation, the transmitting station A transmits the corresponding missed user data frames in the number same as the number of the received NAK control frames, to the receiving station B.
Such conventional method for transmitting NAK control frames has problems described in the following.
That is, despite that the value of the NAK timer is expired for the user data frames of the sequence numbers 4,6,7,10,12 at an equal time, the respective NAK control frames for the respective corresponding user data frames should be transmitted in the conventional method, to accordingly cause some delay. That is, when the NAK timer is expired, the NAK control frames for the respective user data frames not received till that are transferred several times. Then, the transmitting station A retransmits the user data frames by the number of the received NAK control frames. Accordingly, unnecessary delay is caused. For instance, in case the user data frame of the sequence number 4 is not received, the receiving station B transfers the NAK control frame for the sequence number 4 several times when the NAK timer is expired. Thus, a delay time in sending the NAK control frames increases to cause a fall of a throughput per unit time.
A sequential order for transmitting the frames on the traffic channel is as an NAK control frame, a missed user data frame and a new user data frame. Consequently, when one NAK control frame for one user data frame is sent every 20 ms on the traffic channel having many transmissions of the NAK control frames, a point of time in sending the new user data frame low in a prior transmission order is delayed much.
Accordingly, the present invention is directed to a control frame and user data frame transmitting method that substantially obviate one or more of the limitations and disadvantages of the related art.
An object of the present invention is to provide a method for transmitting user data frames and control frames in a mobile radio communication system capable of ensuring a reliability of an NAK control frame transmission.
Another object of the present invention is to provide a method for transmitting user data frames and control frames in a mobile radio communication system capable of preventing a transmission delay of frames.
A further object of the present invention is to provide a method for transmitting user data frames and control frames in a mobile radio communication system capable of heightening a throughput per unit time.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure as illustrated in the written description, as well as the appended drawings.
To achieve these and other advantages, and in accordance with the purpose of the present invention as embodied and broadly described, it is considered as follows.
It is desirable to send NAK control frames more than the total number of the retransmission of user data frames if the transmission link of the user data frame is more reliable. The opposite case may occur too, that is, there are some other cases where an asymmetric RLP retransmission is also desirable. For instance, we known that it is crucial that the NAK control frames are transmitted as early as possible. However, when it is tried to send many different control frames including the NAK control frames in a CDMA system in which many RLP entitles can exist in a mobile station, congestions may be caused in a mapping layer or an MUX/QoS sublayer. In this case, it is needed that the NAK control frames be transmitted over an SCH or the transmission number of the NAK control frames be reduced if a transmission link is in a good condition in terms of frame error rate.
In the inventive method, at equal time when a timer for an NAK is expired, series numbers of missed user data frames are loaded on one NAK control frame and this NAK control frame is transmitted to a transmitting station from a receiving station.
At this time, the retransmission number of the missed user data frames is variable according to a state of a corresponding traffic channel, and such retransmission number is indicated on the NAK control frame.
The transmission number of the same NAK control frames is also variable according to a state of a corresponding channel, and a series number of the NAK control frame, capable of identifying the transmission number is also represented on that NAK control frame.
In a structure of the NAK control frame in accordance with the present invention, there are provided a field NAK_SEQ indicating series numbers of NAK control frames, for checking a duplication, a control field CTL representing NAK control frames requiring a retransmission of missed user data, and a field RE_NUM providing the retransmission number of missed user data frames. Also, the transmission number of that NAK control frames is variable according to the number of user data frames requesting its retransmission.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.